dominica is a great eco sightseeing island. you could spend a week and not see everything. minimal shopping however. we usually take the cruise ship tour but not in Dominica.
you want to use Kens hinterland tours the link is below
ken is great, we had a van for four of us and a great driver/guide. see the web site for suggested tours or ken will custom design one for you. research the islandlnd you will love it. it is the only island that still looks the way it did when discovered by columbus.